No one was injured. The robbery was reported about 9:30 p.m. at a store on the 1500 block of Discovery Bay Boulevard, according to Contra Costa Sheriff's spokesman Jimmy Lee.

Deputy sheriffs who responded to the call searched for the suspect, aided by a K-9 unit and a California Highway Patrol helicopter, but did not find him, Lee said. He was described as a white man in his early 20s, wearing a white mask and a baseball cap.

Anyone with information on the robbery is asked to call the Sheriff's office at 925-646-2441.